The scale of animal production operations continues to expand as a means of increasing the efficiency, consistency, and reliability of the production of animal-related products. As the size of production facilities expand, the importance of providing containment facilities with fresh air and treating the facility's exhausted air also increases. Air exhausted from these facilities has excessive levels of particulate dust (mainly comprising manure) and ammonia gas (NH3).
The prior art includes multiple systems for treating air exhausted from animal containment facilities, including the inventor's previous U.S. Pat. No. 7,194,979 titled METHOD AND DEVICE FOR SCRUBBING AMMONIA FROM AIR EXHAUSTED FROM ANIMAL REARING FACILITIES (hereinafter “Moore '979), which is hereby incorporated by reference. As described in Moore '979, air exhausted from an animal rearing facility is passed through a single stage scrubber where it is brought into contact with a solution comprising a salt of an acidic proton donor. The proton donor solution converts the volatile ammonia from the exhaust gas to non-volatile the ammonium (NH3+H+→NH4+) and thereby removes the ammonia from the air.
Although the system describe in Moore '979 is very effective, the acidic salts (that comprise the proton donors) described by Moore '979 are problematic. The iron and aluminum salts react with ammonia to form iron and aluminum oxides and hydroxides, which can plug the pipes and cool cell material in the scrubber. Calcium and magnesium proton donors also cause the formation of solids and they lack sufficient acidity to effectively trap the ammonia. Sodium proton donor solutions (particularly sodium bisulfate, NaHSO4) very effectively remove ammonia from the exhausted air, however using the sodium proton donor solution with ammonia results in a scrubber solution that is rich in nitrogen but has extremely high concentrations of sodium. The high concentrations of sodium will eventually cause sodic soil conditions, and thereby limit the long term use of the scrubber solution as a fertiliser.
Strong acids such as hydrochloric, nitric, sulfuric, and phosphoric acids function effectively to remove the ammonia from the exhausted air, however there is a significant safety risk associated with storing, applying, and handling these materials in a farm environment. The strong acids are generally required to balance the alkalinity of the exhausted air.
The need exists for a proton donor solution that effectively reduces ammonia (among other things) from exhausted animal containment facilities without clogging or damaging scrubber components. When the proton donor solution is combined with ammonia, the resulting nitrogen-rich scrubber solution should be usable as an effective fertilizer. The proton donor solution material should also be safe and easy to handle by farm personnel with little or no training. There is also a need for reducing greenhouse gases from the exhausted air, as well as particulates—including manure and bacteria, fungi, and viruses.
The system described herein comprises a two stage exhaust scrubber system wherein the carbon dioxide, particulate matter, and alkalinity of the exhaust air is reduced by a first scrubber, and a second scrubber reduces the amount of ammonia and volatile organic compounds (VOCs) in the exhaust air. The inventor has found that potassium bisulfate (KHSO4) effectively functions as a proton donor scrubber solution to remove ammonia from exhausted animal containment facility air, and neutral salts of calcium (e.g. gypsum in combination with a water) effectively functions to reduce carbon dioxide from the air.
Combining the potassium bisulfate scrubber solution with exhausted ammonia yields a scrubber solution that is rich in nitrogen and potassium and consequently makes an excellent fertilizer. Potassium bisulfate can be stored and handled as a “dry” acid and therefore poses a reduced risk of accident or injury to farm personnel. Combining the neutral calcium salt with carbon dioxide and manure dust yields a scrubber solution that includes the fertilising qualities of manure and is also has a high lime content.